Illegal drug in jacket (6)

I believe the answer is:

reefer

I'm a little stuck... Click here to teach me more about this clue!

This clue could be a double definition.

'illegal drug' is the first definition.
'reefer' can be an answer for 'drug' (reefer is a kind of drug). I'm unsure of the 'illegal' bit.

'jacket' is the second definition.
(I've seen this before)

'in' is the link.

Can you help me to learn more?

(Other definitions for reefer that I've seen before include "habit?" , "Easy" , "Unofficial smoking" , "close-fitting garment" , "Warm jacket - cannabis cigarette" .)

I've seen this clue in The Times.

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